This invention relates to a transfer material to be used for image formation according to the heat-sensitive transfer system, particularly to an image-receiving sheet to be used in combination with a heat transfer sheet.
It has been known in the art to obtain an image-receiving sheet by forming a receiving layer by applying and drying a composition for formation of a receiving layer directly or after formation of an undercoat layer or intermediate layer on a substrate sheet.
However, the image-receiving sheet of the prior art does not exhibit satisfactory whiteness of the image-receiving layer, and therefore a color image of high sharpness cannot be obtained easily. Additionally, and also the whiteness of the image-receiving layer is liable to be further lowered by change with lapse of time, whereby there has been the drawback that sharpness of the image immediately after transfer onto the image-receiving sheet cannot be maintained easily.
The composition for formation of the receiving layer used in the prior art comprises generally a thermoplastic resin. These thermoplastic resins, when degradated with heat or light, tend to be degraded in tone by coloration in yellow.
Whereas, as the method for determinating quantitatively the tone of such subject matter, there is the method as defined in JIS-Z8722 and JIS-Z8730.
According to the method as defined in JIS-Z8722 and JIS-Z8730, the tone of a subject matter to be measured is represented by the three values of L, a and b. Here "L" represents lightness, and exhibits higher lightness as this value is greater. On the other hand, "a" represents reddishness, and exhibits stronger reddishness as the value is greater, and deficiency of reddishness when it becomes - (minus), in other words stronger greenishness. Further, the value "b" is an index of yellowishness, and exhibits stronger yellowishness as this value is greater, and deficiency of yellowishness when it becomes - (minus) to become blueish. Colorelessness is indicated when both of a and b are zero.
Whereas, for preventing the inevitable problems of coloration of the image-receiving sheet of the prior art as described above, first, one may consider to add a white pigment in the receiving layer. In this case, the reflectance of the surface can become higher to some extent (namely, L value is increased), but according to this method, the b value becomes also higher, thereby ensuing a new problem of being tinted with yellowishness. For this reason, it appears that whiteness is visually rather lowered. By use of such an image-receiving sheet, the image portion, particularly the highlighted portion, becomes yellowish to lose sharpness, whereby the value as image-receiving sheet cannot but be lowered.